The present invention relates generally to elevator suspension ropes and, in particular, to wear detectors for polyurethane coated suspension ropes.
Steel wire ropes are well known. Steel wire ropes consist of metal strands braided or twisted together to form a rope. Steel wire suspension ropes are used as stationary and as running ropes for many different purposes. Such ropes have the advantage of being inexpensive, durable, and flame retardant. One common use for suspension ropes is in elevator applications. A conventional traction type elevator application includes a cab mounted in a car frame, a counterweight attached to the car frame via the suspension rope, and a machine driving a traction sheave that is engaged with the rope. As the machine turns the sheave, friction forces between the grooved surface of the sheave and the rope move the rope and thereby cause the car frame and counterweight to raise and lower. A control device is included to monitor and control the operation of the machine and the various mechanical components of the elevator application.
Used as either stationary or running ropes, steel ropes can support heavy loads. In the case of running ropes, this tensile loading is complemented by flexural loading that reduces their service lifetime due to the number of load ranges in which they operate. The coefficient of friction or frictional value between the metal drive pulley and the steel rope is generally so low that the frictional value must be increased by different measures. These measures can include special groove shapes or special groove linings in the drive pulley, or through an increase of the loop angle. In addition, the steel rope acts as a sound bridge between the drive and the elevator car, which entails a reduction in travelling comfort. These running steel wire ropes, moreover, do not last forever, as mechanical wear of the ropes is an obvious consequence of their continual operation. Due to increasing stresses, friction and wear, wire fractures gradually occur in the bending zones. These fractures occur due to a combination of different loads on the elevator ropes, low tension stresses, and high pressures at high cycle rates. The safety of the steel wire rope condition is monitored in order to detect an operationally critical state of their wear, in advance of failure of the ropes. This is known in the art as controllable wire rope failure, which means that the danger-free remaining period of use can be read from an outward degree of wear of the steel wire rope. Once a predetermined amount of wear has occurred, the steel wire rope is replaced. In addition, steel wire ropes require lubrication. The steel wire ropes are treated with an oil lubrication that ultimately can be deposited on the elevator car frame and equipment.
One known method of solving the friction, travelling comfort, and wear resistance problems is to construct ropes of synthetic fiber. Synthetic fiber ropes, however, are not always desirable because they are relatively expensive compared to a steel rope. Another known method of solving the friction, noise, and wear resistance problems is to provide a coating, or sheath. The sheath allows smoother and quieter elevator operation in that there is less friction when the rope moves across the pulleys and sheaves as compared to the metal-to-metal contact with a steel rope that does not have a sheath. The sheath is typically formed from a synthetic plastic material, such as polyurethane, and its purpose is to provide wear resistance for the wire rope. Another benefit is that the sheath provides a sacrificial wear material so the metallic drive pulley wear is at least reduced and at best eliminated. Once the sheath has sustained a predetermined amount of wear, like conventional steel wire ropes, the rope is replaced.
The current means of wear detection of polyurethane type covers is to visually inspect on a periodic basis for cover wear or damage. This is a time-intensive operation that requires the elevator to be placed out of service while maintenance personnel perform the visual inspection of the entire suspension rope. It is desirable to reduce both the amount of time and the manpower necessary to determine the wear or damage of the polyurethane cover of the suspension rope. It is also desirable to monitor the wear of the polyurethane sheath and to provide a notification to the operator of an elevator as soon as abnormal or increased wear on a suspension rope is detected.
It is an object of this invention, therefore, to detect, by either electrical or optical means, the wear on the rope sheath in order to determine when the rope needs replacement. It another object of this invention to provide an inexpensive means for determining wear or damage on a suspension rope and to be able to determine the amount of wear or damage remotely.
The present invention concerns an apparatus for detecting wear in suspension ropes with polyurethane sheaths when used with an elevator assembly.
In a preferred embodiment, the present invention contemplates detecting wear of the non-conductive polyurethane sheath by providing a sensing circuit with any grounded object such as a drive sheave or an idler sheave. When the electrically conductive strands of the rope make contact with the drive sheave or idler sheave through the worn non-conductive polyurethane cover, the sensing circuit signals the control device to take the car out of service once the rope becomes electrically grounded.
In an alternative embodiment, the present invention contemplates detecting wear of the non-conductive polyurethane sheath by providing a proximity sensor that contacts the polyurethane sheath and actively measures the sheath thickness as a distance to the rope strands. The sensor signals the elevator control device to take the car out of service once a predetermined cover thickness wear has occurred.
In another alternative embodiment, the present invention contemplates detecting wear of the non-conductive polyurethane sheath by providing layers of different colors. The polyurethane sheath changes color when an outer layer of one color is worn away to expose an inner layer of another color indicating that predetermined wear has occurred. An optical sensor is then utilized to detect the inner layer color and signal the control device to take the car out of service.
In each of the above-described embodiments, the present invention provides a sensor means for the active monitoring of the wear of the rope polyurethane sheath at all times. The present invention provides multiple means for remotely monitoring the rope polyurethane cover wear, with each means utilizing low cost technology components. The present invention is also able to detect both complete and partial wear of the rope polyurethane cover. In addition, the present invention allows the rope polyurethane cover wear to be visually inspected without the use of measurement tools.